01-Jun-2002 Rev. A

Page

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Any changing of specification will not be informed individual

Elektronische Bauelemente

ST2123

CMOS Positive

Voltage Regulator

ST2123-AD

Adjustable

3BAD2

XXXX

Ordering Information(contd.)

Part Number

Marking

Output Voltage

Part Number

Marking

Output Voltage

Detailed Description

The ST2123 of COMS regulators contain a PMOS pass transistor,voltage reference, error amplifier,over-current protection and

thermal shutdown and Power Good detection circuitry.The P-channel pass transistor receives data from the error amplifier,

over-current shutdown,and thermal protection circuits. During normal operation, the error amplifier compares the output voltage to

Over-current and Thermal shutdown

circuits become active when the junction temperature exceeds150 C,

or the current exceeds 300mA.During thermal shutdown,the output voltage remains low. Normal operation

below 120 C. The ST2123 switches from voltage mode to current mode when the load exceeds

This prevents over-stress.The ST2123 also incorporates

o

o

current fold-back to reduce power dissipation when

This feature becomes active when the output

Full current is restored when the voltage exceeds 0.8 volts.

External Capacitors

The ST2123 is stable with an output capacitance to ground of 2.2uF or greater. Ceramic capacitors have the lowest ESR, and will offer

the best AC performance. Conversely, Aluminum Elertrolytic capacitors exhibit the highest ESR, resulting in the poorest AC response.

Unfortunately, large value ceramic capacitors are comparatively expensive. One option is to parallel a 0.1 uF ceramic capacitor with a

10 uF Aluminum Electrolytic. The benefit is low ESR, high capacitance, and low overall cost. A second capacitor is recommended

between the input and ground to stabilize Vin. The input capacitor should be at least 0.1uF to have a beneficial effect. All capacitors

should be placed in close proximity to the pins. A "Quiet" ground termination is desirable . The can be achieved with a "Star" connection.

Enable

The Enable pin normally floats high. When actively, pulled low, the PMOS pass transistor shuts off, and all internal circuits are powered

down. In this state, the quiescent current is less than 1uA. This pin behaves much like an electronic switch.

Note:

2.To prevent the Short Current protection feature from being prematurely activated,

the input voltage must be applied before a current source loas is applied.

a precision reference.

junction temperature drops

is restored when the

the rated output current.

the output is short circuited.

drops below 0.8 volts, and reduces the current flow by 65%.

Power Good

The ST2123 includes the Power Good feature. When the output is not within

10% of the specified voltage, it pulls low.

This can occur under the following confitions:

1. Input voltage too low

2. During over-temperature

3. During over-current

4. If output is pulled up

(note: PG pin is an open-drain output)

±